Education and Achievements

Dr. Art Greenberg gave the introductory talk at the symposium honoring the fiftieth anniversary of the James Flack Norris Award in Physical Organic Chemistry at the National ACS Meeting in Dallas, TX on March 17, 2014. Dr. Greenberg is third from the right. Norris winners include (Left to Right): Hans J. Reich, John I. Brauman, Michael R. Wasielewski, Kendall N. Houk, John D. Roberts, Matthew S. Platz, Ned A. Porter, Andrew Streitwieser, Jr., Paul von Ragué Schleyer, and John E. Baldwin.

Research Interests

Physical organic chemistry and environmental organic chemistry. Emphases include strained organic molecules such as bridgehead bicyclic lactams, having twisted amide linkages, and epoxyoxepins of possible relevance to benzene metabolism. Interests include airborne carcinogens such as polycyclic aromatic hydrocarbons (PAH) and their derivatives.

Current Research Interests

A. 2,3-Epoxyoxepins as Potential Benzene MetabolitesBenzene is a human carcinogen that is primarily metabolized in the liver. Although most absorbed benzene is metabolically functionalized to phenol which is further metabolized (Phase I) and conjugated (Phase II), a small but significant fraction is metabolically ring-opened to E,E-muconic acid (HOOC-CH=CH-CH=CH-COOH). At least two groups of researchers established some two decades ago that muconaldehyde (OHC-CH=CH-CH=CH-CHO) is the metabolic precursor. How is muconaldehyde formed metabolically. Follow the suggestion of Davies and Whitham in the 1970s we are the first to synthesize and spectroscopically observe epoxidation products of oxepins we term 2,3-epoxyoxepins. These compounds rapidly ring open supporting a logical pathway from benzene to muconaldehyde. Proposed studies will investigate the mechanism of ring opening of 2,3-epoxyoxepins to the corresponding dicarbonyl compounds. In addition, incubation with cytochrome P450 enzymes in collaborative studies will be investigated in order to test the biological significance of this pathway.

B. Bridgehead Bicyclic LactamsThe amide (or peptide) linkage (C-NR-CO-C) normally maintains planarity with a N-CO rotational barrier of about 20 kcal/mol (about one-third the rotational barrier of a C=C bond). Small bridgehead bicyclic lactams such as 1-azabicyclo[2.2.2]octan-2-one or 2-quinuclidone (see Chemical & Engineering News, June 12, 2006, p. 9) have substantially twisted and distorted amide linkages. The results include a loss (or partial loss) of classical resonance energy and changes in chemical properties such as changing the site of protonation or alkylation from oxygen, as in unstrained amides and lactams, to nitrogen in the highly twisted species. Our studies, both experimental and computational, examine the chemical consequences of such distortion upon the site of protonation and the possibility of producing an entirely new functional group: amide N-oxides. Our studies also focus on the potential syntheses of "hyperstable" bridgehead lactams.

C. Polycyclic Aromatic Hydrocarbons (PAH) and Derivatives on Air ParticulatesPolycyclic aromatic hydrocarbons (PAH) are ubiquitous by-products of combustion or pyrolysis of organic substances. They are found on airborne particulate matter in concentrations typically on the order of ng per cubic meter. Nitro-derivatives of PAH, may be formed as primary pollutants (e.g. 1-nitropyrene) in the combustion of diesel fuel, or as secondary pollutants (e.g. 2-nitropyrene) from PAH reacting under atmospheric conditions. Nitro-PAH are usually found in pg per cubic meter concentrations but they are very strong mutagens. Our research employs HPLC with diode array UV and fluorescence to analyze PAH, nitro-PAH and other derivatives. One goal will be to assess the levels of these carcinogens and mutagens in airborne particulates obtained in downtown San Salvador (El Salvador) where very poorly maintained diesel buses are the primary mode of transportation. Such data will be employed in human risk assessment studies.

131. A. Greenberg, James Flack Norris: His Early Contributions to Physical Organic Chemistry, In T. Strom and V. Mainz (Eds), Fifty Years of the James Flack Norris Award. The Foundations of Physical Organic Chemistry, ACS Symposium Series, in press.

Recent Books

Greenberg, A., A Chemical History Tour, John Wiley & Sons, New York, 2000

Greenberg, A., The Art of Chemistry, John Wiley & Sons, New York, 2003